The present invention refers to a clamping apparatus for fixing and non-rotatably clamping threaded shafts, particularly threaded shafts used as electrodes for eroding threads.
In order to fix and clamp, respectively, threaded shafts used as electrodes for eroding threads, usually clamping devices in the kind of split chucks or collet chucks are used that are inserted in a corresponding chuck holding device and clamped therein. The threaded shaft to be firmly held in place is inserted into the central opening of the split chuck and clampingly fixed in the desired position. This kind of fixing has two fundamental disadvantages. First, only the crests of the thread convolutions rest against the inner wall of the split chuck and are clamped therein, with the result that the thread convolutions could be damaged, particularly in the case of V-threads. Second, the position of the thread with regard to the split chuck and the chuck holder, respectively, is not exactly defined. The result is that the position of the thread and the thread convolutions, respectively, with regard to the chuck holder changes upon a positional adjustment of the threaded shaft, for instance an axial re-adjustment, required due to wear. However, since it is common practice in the process of eroding threads to initially roughing a number of threads with a first portion of the threaded electrode shaft and then, after positionally adjusting the threaded electrode shaft, to finally erode the pre-roughed thread with a second, unused portion of the threaded electrode shaft, the danger exists that the positions of the thread convolutions of the afore mentioned first portion of the threaded electrode shaft and of the afore mentioned second portion of the threaded electrode shaft do not coincide. The result is that no precise thread flanks can be realized; the final thread does not fulfill high quality standards. Thereby, it is understood that the used portion of the threaded electrode shaft is cut off before a new, unused portion of the threaded electrode shaft is applied.
U.S. Pat. No. 2,629,277 discloses a stud bolt wrench used for inserting and removing stud bolts. The wrench comprises a body provided with an axial base bore and a base portion having an essentially coaxial counterbore extending along approximately 180xc2x0 of the periphery. Moreover, the base portion has a transverse slot crossing both the base bore and the counterbore. For fixing the stud bolt, a two-part clamping set is provided. The clamping set consists of a stationary part and a movable part, whereby both parts are provided with thread convolutions for engaging the stud bolt. The stationary clamping part is inserted into the counterbore, while the movable clamping part is received in the slot. The two clamping parts are biased by means of a spring in such a way that a stud bolt received in the clamping set is clampingly fixed therein.
The German Patent No. 288,152 discloses a tool for inserting and removing stud bolts. This tool consists of an outer housing provided, on its inner side, with several eccentric, curved surfaces. Received in these curved surfaces are jaws provided with inwardly protruding catches. The catches are provided with thread convolutions for fixing stud bolts. The jaws are held in their positions by means of springs. In order to fix a stud bolt in the tool, the outer housing is rotated with regard to the jaws. Thereby, the jaws are moved radially inwardly under the influence of the eccentric, curved surfaces, such that the thread convolutions of the jaws engage the corresponding thread of the stud bolt.
Finally, U.S. Pat. No. 2,073,274 discloses a stud screw wrench having a hexagonal housing which is provided with a central aperture delimited by four cam-shaped surfaces. Inserted into that aperture is a sleeve having four slots, whereby the sleeve is provided with an inner thread for fixing a stud bolt. The sleeve is divided into four sections by means of the afore mentioned slots. The four sleeve sections are pressed inwardly upon rotating the housing with regard to sleeve the under the influence of the cam-shaped surfaces. In this way, a stud bolt received in the tool is clampingly fixed.
A fundamental disadvantage of the afore mentioned devices can be seen in the fact that the position of a threaded bolt or shaft is not exactly defined nor can be exactly predicted. The reason is that the position of the bolt or shaft with regard to the clamping device depends on the fact, in the case of devices provided with rotating clamping jaws or elements, with how much torque the clamping jaws have been tightened to bring them into their clamping position and in what final position they are.
On the other side, the afore mentioned devices have no provisions or means to align them and, thereby, the bolts or shafts received therein, in such a way that both the axial position and the angular orientation of the bolt or shaft is precisely defined.
It is an object of the invention to provide a clamping apparatus for fixing and non-rotatably clamping threaded shafts that avoids the afore mentioned disadvantages, i.e. to provide a clamping apparatus in which a threaded shaft can be fixed quickly, easily and with high, repeatable accuracy.
In order to meet this and other objects, the invention provides an apparatus for fixing and non-rotatably clamping threaded shafts comprising a hollow tubular housing having a central longitudinal axis. The hollow tubular housing comprises an aperture extending in radial direction with regard to the central longitudinal axis and has a rectangular cross sectional shape. A clamping element is slidably received in that aperture and has a front face provided with thread convolutions. An operating element is provided to slidably move the clamping element received in the aperture towards the central bore and to lock a threaded shaft inserted into the central bore with high positional accuracy and repeatability.
Due to the rectangular shape of the aperture and the clamping element, it is ensured that the position of the clamping element with regard to the clamping apparatus does not change, with the result, that a threaded shaft is clamped in the apparatus always in exactly the same axial position.
Preferably, the housing of the apparatus is provided with a reference surface portion, allowing an exact alignment of the clamping apparatus as a whole, and thereby of course also of the threaded shaft clamped therein, with regard to, for instance, a machine tool.